Water stop compositions are normally extruded in the form of elongated ropes or tapes and are typically used as a gasket or seal in the joints or gaps between adjacent concrete or metallic building panels or structure. A variety of rubber, plastic, and asphalt water stop compositions have been used throughout the years.
Desirably, the water stop should be swellable so that upon hydrolysis it will expand to cover the surface area of the joint or gap in which it is placed. In this manner, the water stop can then adequately perform its intended function of acting as a water seal to prevent water penetration into the gap or joint.
To this end, a variety of compositions including water soluble clays, such as the bentonites, and a plurality of elastomeric materials has been proposed. For example, U.S. Pat. No. 4,668,724 discloses water stop compositions comprising non-hydrated bentonite clay contacted with a polypropene and/or polybutene tackifier. Purportedly, the polypropene an/or polybutene tackifiers increase the swelling capacity of the bentonite while providing sufficient tack or adherence characteristics to the water stop.
European Patent Application 0 037 717 discloses an aqueously swelling water stopping composition which comprises polyisobutylene elastomer, silicates and bentonite. The silicate components are apparently included to increase the swelling effects of the compositions, with volumetric swelling increases on the order of 80% and greater for 1 day tests being reported.
Other clay based water swellable compositions are taught for example in U.S. Pat. Nos. 4,624,982 (Alexander); 4,534,925 (Harriet); 4,534,926 (Harriet); 4,787,780 (Harriet); 4,693,923 (McGroaty); 4,344,722 (Blais); 4,209,568 (Clem); 4,613,542 (Alexander); and 4,501,788 (Clem).
Despite the efforts of the prior art, and in contrast to the desirability for high volumetric expansion as taught in the above European application, it has been found highly desirable to provide a "controlled expansion" water stop material. More specifically, it has been found that virtually uncontrolled or high expansion water stop compositions deteriorate and fail under actual usage conditions. At the same time however, the compositions should be capable of swelling to a limited degree so that they may adequately fill the structural gaps or joints into which they are placed to provide the desired water sealing function.